Improved performance and miniaturization are needed to meet the ever-increasing demands of devices used in ultrahigh frequency (UHF), L-band, and S-band applications, which are of particular interest in a variety of commercial and defense related industries. As a critical component in radar and modern wireless communication systems, antenna elements with compact size are constantly being developed. It has, however, been challenging to develop ferrite materials for use in such high frequency applications. Known ferrite materials exhibit relatively high magnetic losses at high frequencies, which have not met the need for the design of a practical antenna.
More generally, in modern wireless communication systems the demand for high performance devices of miniaturized structure is ever increasing. A material exhibiting high permeability with equivalent permittivity and having low magnetic and dielectric losses is ideal as an antenna substrate material. Such materials enable miniaturization, while concomitantly maintaining or enhancing antenna gain and bandwidth. Spinel ferrites with high permeability values, such as NiZn ferrites, have been widely used for high frequency applications. However, these ferrites exhibit relatively low cutoff frequencies that prevent their use above 0.3 GHz. Some hexaferrite materials, such as cobalt substituted barium Y-type (Co2Y) and Z-type (Co2Z) hexaferrites have much higher ferromagnetic resonance frequencies above 1.0 GHz due to their high magnetocrystalline anisotropy fields and high permeabilities. Accordingly, the use of magnetodielectric substrates with values of the permittivity ε′ equivalent to the permeability μ′ is popular due to the ease in impedance matching between substrate and free space among other benefits. However, it is very challenging to obtain low magnetic and dielectric losses and high permeability of the dielectric substrates. It has been reported that Co2Y has ε′ of 15-20 and μ′ of 2-3, while Co2Z has ε′ of 12 and μ′ of 18-19, but magnetic loss of the single phase Y- or Z-type ferrite is still considerably high (loss tangent, tan δμ>0.5) at f>0.5 GHz.